Add element to array if not exists, increment a value in the element if element already exists in th-CodePudding

The mongodb collection looks like the array below

[
  {
    "_id": 1,
    "arr": [
      {
        "key": "abc",
        "val_a": 2
      }
    ]
  },
  {
    "_id": 2
  }
]

What I want to do is increment 1 to the element in arr array with key def. If the element with key def is not in the array arr, I want to add a new element like below to arr

{
    "key": "def",
    "val_a": 1
}

I tried

db.collection.update({
  "_id": 1,
  "arr.key": "def",
  
},
{
  "$inc": {
    "arr.$.val_a": 1
  }
})

But it is not adding the new element. The result is like

[
  {
    "_id": 1,
    "arr": [
      {
        "key": "abc",
        "val_a": 2
      }
    ]
  },
  {
    "_id": 2
  }
]

What I am expecting is something like this:

[
  {
    "_id": 1,
    "arr": [
      {
        "key": "abc",
        "val_a": 2
      },
      {
        "key": "def",
        "val_a": 1
      }
    ]
  },
  {
    "_id": 2
  }
]

I want to do it in one operation as I am intending to do is a BulkWrite operation with UpdateOneModel.

CodePudding user response：

Query

finds the _id
new-member you set any document to add
if arr is not array make it an empty array, so concat to work later
check if it exists
if not exists, add to the end of the array
else map to find it and increase its val_a

PlayMongo

*this is pipeline update, to do it with 1 query, alternative way is with 2 queries, one to check if it exists, and the second to $push (if not exists) or to $set with arrayFilters.
(you would had to send 2 queries and write 3 queries, and its not atomic safe)

update(
{"_id": {"$eq": 1}},
[{"$set": {"new-member": {"key": "abc", "val_a": 1}}},
 {"$set": {"arr": {"$cond": [{"$isArray": ["$arr"]}, "$arr", []]}}},
 {"$set": 
   {"not-exists": 
     {"$eq": 
       [{"$filter": 
           {"input": "$arr",
            "cond": {"$eq": ["$$this.key", "$new-member.key"]}}},
         []]}}},
 {"$set": 
   {"arr": 
     {"$cond": 
       ["$not-exists", {"$concatArrays": ["$arr", ["$new-member"]]},
         {"$map": 
           {"input": "$arr",
            "in": 
             {"$cond": 
               [{"$eq": ["$$this.key", "$new-member.key"]},
                 {"$mergeObjects": 
                   ["$$this", {"val_a": {"$add": ["$$this.val_a", 1]}}]},
                "$$this"]}}}]}}},
 {"$unset": ["new-member", "not-exists"]}])